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February 2001

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Subject:
From:
Jim Kittel <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 6 Feb 2001 08:26:51 -0700
Content-Type:
text/plain
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text/plain (142 lines)
Nicolas,
If the paste looks good after printing and has not bridged or smeared after
the parts are placed, the paste may be 'hot slumping' inside the reflow
oven.  You can test this by printing a board and then placing it into an
oven at 100 deg C. for about 10 minutes.  If the paste moves significantly,
you have bad solder paste.
Jim Kittel

 -----Original Message-----
From:   Nicolas Ortiz [mailto:[log in to unmask]]
Sent:   Tuesday, February 06, 2001 7:45 AM
To:     [log in to unmask]
Subject:        Re: [TN] QFP144 solder bridging

Stencil is OK. No changes in design.



                    Trevor
                    Goddard              To:     [log in to unmask]
                    <tgoddard@XLT        cc:
                    EK.COM>              Subject:     Re: [TN] QFP144 solder
bridging
                    Sent by:
                    TechNet
                    <[log in to unmask]
                    ORG>


                    02/06/01
                    06:03 AM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum.";
                    Please
                    respond to
                    Trevor
                    Goddard






Nicolas
 I have a couple of questions for you.
 Is this a new board or a new Rev of an existing product?
 Did you review the stencil design or did you actually have the stencil
measured?
 I got caught one time when I was given a new Rev of an existing product.
We
had a couple of QFPs .20mm and a .50mm pitch  that were shorting out like
crazy, which was never a problem on the previous Rev. I questioned the guys
that ordered the stencil and the layout guys about what specs the stencil
was ordered to and if there had been a footprint changed. The answers to my
questions was that nothing had changed, but I could still not fix the
problem with process changes. Finally we were able to get the stencil
measured and the pad sizes measured and found out that the apertures on
some
components were 100% of the pad size and another was a tiny bit bigger than
pad size.
 My guess is, if nothing has changed in your manufacturing process i.e..
screen printing parameters, reflow profile and your placement is good than
something may have changed in the design side.

Trevor
-----Original Message-----
From: Nicolas Ortiz [mailto:[log in to unmask]]
Sent: Monday, February 05, 2001 3:45 PM
To: [log in to unmask]
Subject: [TN] QFP144 solder bridging


Currently we are experiencing solder bridging on a 0.5mm pitch,  LQFP,  144
leads. I already reviewed the stencil design, screen printer parameters and
reflow profile. Everything is OK. We have HASL boards. Our current process
outputs 38 dpmo's. My concern is if I reduce more the apertures, I have the
risk to have solder open or insufficient solder, instead of bridging. Does
anybody has some input? What dpmo's do you have?

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